Mueller R, Zhang S, Klink M, Bäumer M, Vasenkov S
Department of Chemical Engineering, University of Florida, Gainesvlle, FL 32611, USA.
Phys Chem Chem Phys. 2015 Nov 7;17(41):27481-7. doi: 10.1039/c5cp04609b.
Pulsed field gradient (PFG) NMR was applied to measure tortuosity factors for carbon dioxide diffusion in the Knudsen and gas regimes inside monoliths of a samaria-alumina aerogel catalyst, a high porosity material containing micropores in addition to meso- and macropores. The apparent tortuosity factor obtained from PFG NMR measurements for the Knudsen diffusion in the meso- and macropores of the catalyst has an unexpectedly large value of approximately 6 if carbon dioxide adsorption in the micropores and other types of surface adsorption sites of the catalyst is ignored. At the same time, the corresponding apparent tortuosity factor in the gas regime was found to be around 2. Application of a proposed model which describes fast molecular exchange between the surface adsorption sites and the main pore volume of the catalyst yields corrected tortuosity factors which depend only on the pore system geometry. Using this model, the corrected tortuosity factors were found to be around 2 for both diffusion regimes, in agreement with the expectations based on a high porosity of the studied catalyst.
采用脉冲场梯度（PFG）核磁共振技术来测量二氧化碳在氧化钐 - 氧化铝气凝胶催化剂整体材料内部的克努森扩散区和气体扩散区中的扩散迂曲因子，该催化剂是一种高孔隙率材料，除了中孔和大孔外还含有微孔。如果忽略催化剂微孔中的二氧化碳吸附以及催化剂其他类型的表面吸附位点，通过PFG NMR测量得到的催化剂中孔和大孔内克努森扩散的表观迂曲因子意外地高达约6。同时，发现气体扩散区相应的表观迂曲因子约为2。应用一个描述表面吸附位点与催化剂主孔体积之间快速分子交换的模型，得到的校正迂曲因子仅取决于孔系统几何形状。使用该模型，发现两种扩散区的校正迂曲因子均约为2，这与基于所研究催化剂的高孔隙率的预期相符。
